Studying effect of cell wall's carboxyl-carboxylate ratio change of Lemna minor to remove heavy metals from aqueous solution.

The pre-treated Lemna minor can remove Hg(II), Cr(III), Cr(VI) and Cu(II) from the aqueous solution. The concentration determination of carboxyl and carboxylate groups and its rule to change the metal ions uptake was done by the curves of the potentiometric titration. It was shown that the removal percent of the heavy metal ions (Co=1.00 mM) increased 25.1, 26.0, 17.2 and 24.1% for these ions, respectively, with increasing the carboxylate from 0.92 to 2.42 mmol/g L. minor and then activating by the activator chloride salts. The removal percent of these ions was decreased 33.1, 27.5, 20.7 and 15.01%, respectively, with increasing the carboxyl from 1.50 to 2.41 mmol/g L. minor, inspite of activating by the chloride salts. The enthalpy change (DeltaH) was -27.43, -25.94, -28.12 and -22.27 kJ/mol and the entropy change (DeltaS) was 81.3, 79.9, 86.1 and 67.7 J/mol K, by activated biomass, respectively. L. minor removed these heavy metals corresponding to pseudo-second-order kinetic model that the activation energy (E(a)) was obtained 18.59, 15.93, 20.36 and 21.12 kJ/mol by the activated and 23.02, 22.27, 23.98 and 24.46 kJ/mol by the reference biomass to uptake Hg(II), Cr(III), Cr(VI) and Cu(II), respectively.